Satish,

I repeat - the 'sizes' of atoms in vacuum are not changed from those in 1bar gas.

If they *were* different, they would have different excitation energies and absorption wavelengths - and that is seen to not be the case.

Thanks again sir for your answer

I have seen testing of air compressor at 600 ponds per square inch. This is too much pressure ,how molecules are resisting the effects of extreme pressure changes without affecting their own size.

In hydraulic crane and lifts there is too much pressure in the system .

Satish,

Remember, in a gas the molecules are separated by many many times their diameter - that's the definition of a gas. In air at 1bar the spacing is >500 times the diameter of any molecule.

So a mere 600psi (40 bar, say), reduces the space between molecules by a factor of less than 4.

Now the molecules (still utterly unchanged in shape or size) are spaced, on average, by distances about 100 times their diameters.

You need astrophysical pressures (say, the core of a star) before molecules are pressed against each other, and they then distort.